Alcohols are organic compounds having the functional hydroxyl group (—OH) attached to one or more saturated carbons, containing one or more carbon atoms. The best known compound of this class is ethanol or ethyl alcohol. The latter can be found in alcoholic beverages, in cleaning products, in pharmaceutical products, such as chemical solvent and also in its most voluminous application as fuel for internal combustion engine.
More than 90% of ethanol is produced worldwide from fermentation of sugars coming from direct sources such as sugar-cane, molasses and fruit pulps, or obtained directly by hydrolysis of starch and cellulose. In these amylaceous, feculent and cellulosic groups, a wide variety of grains stand out, such as corn, manioc, other tubercles, sorgo, wheat, barley, sugar-cane bagasse, potato, whey, etc.
The manufacture of ethanol by fermentation and distillation is basically divided into 4 phases: preparation of the raw material or saccharification, liquefaction, fermentation and distillation. For the productions of wine and beer there is no distillation phase. The preparation of the raw material, such as grinding, crushing and leaching, comprises passing the source of sugar, starch or cellulose through processors. In the second phase, one obtains diluted substrates that can either be processed in the fermentation or passed through other intermediate processing of breaking the amylaceous or ellulosic chains into sugar molecules by effect of hydrolysis. The sugary juice or wort obtained is led to fermentation.
The fermentation phase comprises adding microorganisms, fungi or bacteria, which transform the sugars into alcohol by a number of enzymatic reactions. After this process, on industrial scales, which are characterized by periods of fermentation as shown in Table 1, the fermented wort or wine is obtained.
TABLE 1Typical periods of processes for alcoholic fermentationsWineWeeksBeerWeeksAlcohol - generic productionFrom 10 hours to a few daysFuel alcohol - BrazilFrom 4 to 12 hours
The wine then follows to the fourth and last step, the fractionated distillation, giving rise to hydrated or anhydrous alcohol, depending on the desired and employed characteristics of distillation process and dehydration.
The step that affects the result of the production of alcohol more directly and, therefore, one of the most studied is fermentation, called also alcoholic or ethylic fermentation, in the case of the “rota etilica” (ethylic pathway), which is the biochemical process of transforming sugars such as polysaccharides and monosaccharides such as trioses, tetroses, pentoses and hexoses, among which sucrose, glucose, fructose and xylose stand out, into alcohol. In this process, microorganisms that are responsible for conversion of sugars into molecules of pyruvic acid or pyruvate participate, in a number of intracellular enzymatic reactions, usually called glycolytic pathway. Subsequently, in anaerobic conditions, two other enzymatic reactions take place, which characterize the fermentative process. The first reaction, decarboxylation of the pyruvate, is performed by the enzyme pyruvate decarboxylase, by means of which the carboxyl group is eliminated from the pyruvate molecule, converting it to acetaldehyde molecule, with release of carbon dioxide. The second reaction is the reduction of the ethanol acetaldehyde, performed by the enzyme alcoholic dehydrogenase, completing the fermentative reaction proper.
In general, the fermentative processes are characterized in that they combine substrates, types and strains of microorganisms and especially adequate operational conditions, with a view to maximize the process yield and special characteristics to be transferred to the wort under fermentation, since it is subject to various conditions, both fermentation activating and inhibiting conditions, with the consequent interference in the efficiency and in the quality of the process itself.
The main features that characterize all the reactions, regardless of their being are chemical or enzymatic, are those related to the conversion factors, or more specifically to the efficiencies or yields of these conversions. Evolving from the conception of the spontaneous generation theory, alcoholic fermentation has undergone experimental evaluations and theoretic considerations, being regarded as one of the most successful processes by the prior art. Coupled to the cellular nature of the microorganisms, chiefly of fungi, as eukaryotic single-celled organisms, like cells of animal nature, the study and understanding thereof have been privileged as a means of easy experimental access, in the aerobic and anaerobic respiratory processes, the latter being known also as alcoholic and lactic fermentation, and develop freely.
In 1810, Louis Joseph Gay-Lussac formulated the stoichiometric equation that related the production of ethanol and carbon dioxide from alcoholic fermentation of glucose, which is known to date as:

In 1863, Louis Pasteur introduced the concept and action of microorganisms responsible for conversion of glucose (monosaccharide) to ethanol and carbon dioxide. Thirty-four years later, in 1897, Eduard Buchner fermented sugar at the laboratory without using live microorganisms, introducing the concept of enzymatic action of the fermentative process, illustrated below:
Zymase refers to an enzymatic complex that catalyzes the fermentation of sugar to ethanol and carbon dioxide.
Thus, Buchner presented the hypothesis that yeast cells secreted proteins in the medium, bringing about the fermentation of sugar. Later, it was demonstrated that these fermentation reactions took place inside the yeast cell.
All this development is in agreement with the nature of the efficiency or yield of the transformation of sugars into alcohol, by the verification that, in the natural fermentation conditions, a glucose molecule could produce up to two ethanol molecules and two carbon dioxide molecules. This understanding is quite known as Gay-Lussac (G-L) Yield, its maximum value in the fermentation of glucose being of 51.1% (mass/mass). FIGS. 1 and 2 illustrate the sequence of reactions and the maximum massic yield in the fermentation of glucose.
For the purposes of comparisong, the simplified equations for fermentative process yields of pentoses, hexoses and disaccharide (sucrose) are shown belor. The disacharide sucrose is the predominant sugar in sugar-cane.

Invertase refers to an enzyme that catalysis the hydrolysis of sucrose in hexose, fructose and glucose, the mixture of which is also called inverted sugar syrup.
In the alcohol industry by fermentation of sugars, the pursuit of greater process yields is a constant, involving complete and complex studies and experiments in the physicochemical and biological domains. In a general way, one may write the equation for the complete treatment of the alcoholic fermentation process from the point of view of efficiency ore alcoholic yield as follows:[Sugar]+[Microorganisms]→[Ethanol]+[CO2]+[B-products]+Energy
Herein one understands as maximal real yield the quotient between the concentration of ethanol produced [Ethanol] by the concentration of sugar [Sugar] consumed in the conversion.
During the fermentation process, various microorganism natures may contribute to the consumption of sugar, such as yeast, other than fungi and bacteria. These microorganisms consume the sugary substrate for cellular growth of the species and also in the production of by-products such as acids and higher alcohols, turning to parasitic processes and causing reductions in the fermentation yield.
In 1937, Firmin Boinot patented in France and in 1941 he obtains the U.S. Pat. No. 2,230,318 for a process of carrying out industrial alcoholic fermentations. In the Thirties this process arrives in Brazil, contributing markedly to the increase of fermentation yield, which is now widespread in the world and known by the process name Melle-Boinot, and chiefly but not exclusively applied to fermentations with yeast. A merit of this process is the direct con concurrent reduction of sugar, provided by reuse of the microorganisms and by the treatment and recycle thereof, by centrifugal separation, followed by an acidic treatment for periods of two to four hours in a medium with pH of 2 to 3, in concentrated form, which promotes the drastic reduction of the bacterial population. After this treatment, the yeast milk, as the centrifuged yeast is called, concentrated and treated, if returned to the process. This operation may bring about a sugar consumption reduced to less than 1% (one percent) of the sugar available.
Carbon dioxide as the products released in the decarboxylation of pyruvate is considered as a parallel product of the fermentative process.
Besides the by-products resulting from parasitic processes, as discussed above, other products are generated during the alcoholic fermentation, such as: glycerol, organic acids (succinic, acetic, pyruvic acids, and others) and higher alcohols, acetaldehyde, acetoin, butyleneglycol and other compounds. It is estimated that from 3% to 5% (three to five percent) of the sugar available in the process are consumed in these conversions.
In energetic terms, illustratively, in anaerobiosis conditions, the yeasts deviates its metabolism to the alcoholic fermentation, the ethanol and carbon dioxide being only the two excreta of the whole process. Thus, it follows that:C6H1206+2Pi+2ADP→2C2H5OH+2CO2+2H2O+2ATP (ΔG0=−56 kcal/mole)
On the other hand, in aerobiosis conditions, particularly in the cellular multiplication phase, the yeast carries out respiration. Unlike the fermentation that takes place in its cytoplasm, the respiration, which takes place in the mitochondria, leads to the formation of an amount of ATP (Adenosine Triphosphate) (the energetic exchange means) nineteen times as big as that obtained in the alcoholic fermentation, as illustrated below:C6H1206+6O2+38Pi+38ADP→6CO2+38ATP+6H2O (ΔG0=−686 kcal/mole)
Many actions are still taken during the fermentation process, as initiatives to reduce the consumption of sugars in parasitic processes and undesirable by-products. Control of Ph and temperature of the wort under fermentation, as well as the control of micronutrients and contaminants present, are variables that assume important positions in the process and can stimulate or inhibit the biochemical dynamics.
The low pH of the medium (pH<4.0), particularly associated to high operation temperatures (Top>38° C.), proves to be the factor of greatest physiological interest for the yeast obtained and used at units of industrial production of ethanol, when compared with other inhibitors such as sulfite, lactic acid, alcoholic contents and high concentrations of sugars). The pH 4.5 of the wort, with temperature ranging from 20° C. to 37° C., enables protection against stress factors, and one obtains a higher viability of cell, sprouting, alcoholic yield, regular morphology of the yeasts, decrease in residual sugar and lower release of amino acids in the medium, providing better alcoholic efficiency and stability of the process.
As to the nutrition, the yeast is a heterotrophic microorganism, which feed by absorption. The main nutrients, necessary to the development of the yeasts, so that a satisfactory fermentation can take place, are: (i) nitrogen, a plastic transformation element, important to the growth of the yeast; (ii) phosphorus, energy translocation element—in the absence thereof no fermentation will take place; (iii) potassium, (iv) magnesium; (v) zinc; (vi) manganese, all of which are important in enzymatic reactions; vitamins of the B complex, which are fermentation accelerators, besides the presence of other salts, such as cobalt, copper, sulfur, boron, which are referred-to as micronutrients.
Yeast is also a saprophytic microorganism, which requires an elaborate source of carbon—glucose or another sugar, which supplies chemical energy and the carbonic skeleton of its cellular structures, constituted predominantly by carbon, oxygen and hydrogen. Some vitamins, such as thiamine and pantothenic acid, are also demanded.
As to the source of nitrogen, the yeast uses this element in the ammoniacal (NH4+), aminic (urea) or aminic (in the form of amino acids) forms, with no metabolic capability to make use of nitrate and little or no capability of using proteins from the medium. Since the ammoniacal form is the main one, in the absence thereof the yeast looks for other forms, such as amino acids, thereby causing an increase in the production of secondary components, such as isoamyl, amyl, propyl, isopropyl, butyl, isobutyl alcohols. Phosphorus is absorbed in the form of ion H2PO4-, the predominant form at pH 4.5, whereas sulfur can be assimilated from sulfate, sulfite or thiosulfate. With the use of sulfuric acid in the treatment of yeast, however, as presented above, or in the use of molasses in mixed wort, one avoids the additional use of sulfur, which is lethal to the microorganism when in excess, since present sulfur proves to be sufficient to the process.
On the basis of the foregoing and considering, for instance, the alcoholic fermentation yield with glucose substrate or with directly fermentable sugars, at the maximum theoretical massic G-L yield of 0.511 m/m, according to equation (1), as being 100% maximum theoretic yield, the real fermentative process yield can reach maximum values ranging from 92% to 94% and, moreover, in the most aseptic and controlled productive environments. In unites of lesser control and asepsis, this value may be lower than 85%, which means considerable losses in the productive process.
In this regard, one continuously seeks all and every increase in efficiency, focusing on improved and adequate operational controls, strains and natures of microorganism, selected, combined and modified, with higher productivity and more process resistances. Increases in the fermentative yield of 0.1% to 0.5% already justify considerable investments, in view of the high numbers related to alcoholic production in these industrial media.
Various papers have been developed to improve the yield of a process for producing ethanol, as exemplified hereinafter:
Document U.S. Pat. No. 4,451,566 describes methods and apparatus for the enzymatic production of ethanol from fermentable sugars. A sequence of enzymes for the catalysis of the conversion of sugars into ethanol is retained in a diversity of reaction zones. The fermentable sugar solution passes sequentially through these zones, and the alcohol is recovered in the last zone. In spite of providing a more efficient reaction that the usual process, the present document provides an expensive, complex and difficult-to-maintain solution.
Patent application WO 2007/064546 describes a process for improving the yield of ethanol, decreasing the fermentation time and reducing the formation of by-product by monitoring and controlling the oxy-reducing potential of the fermenter. However, this process requires very specific and difficult-to-maintain monitoring due to the high costs involved, impairing the industrial application of this solution.
Patent document WO 2008/024331 describes a method for magnetic fermentation that includes subjecting a biological material to a static magnetic field for carrying out fermentation of the biologic material in a fermented product. The fermentation reaction may occur in an alkaline or acidic medium, and the magnetic field may be positive or negative. The present document makes use of the static magnetic field to provide an environment more suitable for cell reproduction of the microorganisms. In spite of increasing the number of microorganisms in the alcoholic fermentation, thus increasing the reaction yield, this process needs constant monitoring and total control over the reaction, which makes it excessively expensive and, therefore, economically unfeasible for industrial application.
The prior art also discloses methods for improving the efficiency of carbon capture, as described in U.S. Pat. No. 8,377,665. This method comprises bacterial fermentation, using gaseous substrates according to the Wood-Ljungdahl pathway, which comprises a sequence of enzymatic reactions that take place in bacterial lines.
Although there are many bibliographic references that describe fermentative processes to improve the yield of the production of ethanol, the prior art does not describe specifically the action of hydrogen in a metabolic fermentation process for the purpose of selective production, this process constituting an innovative and original technology. Moreover, all the processes developed have sought the increase in the real yield up to the theoretical limit of the G-L yield.